Gas metal arc welding, commonly referred to as “GMAW” or “MIG” welding, is an electric arc welding process in which the arc is shielded from the ambient atmosphere by a gas or a mixture of gases. Metal is transferred to a workpiece through the arc from a consumable wire electrode. The consumable wire electrode is continuously fed into the arc at a preselected speed corresponding to a given deposition rate for a given wire size.
The optimum type of metal transfer employed with the gas metal arc process is a spray arc where fine metal droplets are transferred in a very controlled manner across the arc gap. Very little spatter is produced using this welding technique. The type of metal transfer can be obtained only with a certain combination of shielding gases and welding parameters and thus is generally produced only within a fairly narrow range of conditions.
Typically gas metal arc welding shielding gases have comprised solely carbon dioxide or have comprised mixtures of argon, carbon dioxide oxygen or helium. Each known shielding gas has a specific known range within which the process with that gas will perform acceptably well. Helium, if employed in the gas mixture, is present in a concentration generally exceeding 20 percent and is used to impart special characteristics to the weld but only when its high cost can be justified.
The use of coated steels has increased over the past few years. Typical problems experienced when arc welding coated steels include heavy spatter, porosity, poor bead appearance, and burn-off and fuming of the coating adjacent to the weld area. In many applications, poor weld bead appearance and poor weld quality are significant problems for the fabricator. Existing shielding gas/wire combinations for gas metal arc welding have not performed well on materials with galvanized, galvannealed or aluminized coatings.
Accordingly, it is an object of this invention to provide an improved gas metal arc welding method which can effectively reduce weld spatter, increase bead wetting and minimize porosity when joining galvanized, galvannealed or aluminized steels. This overall improvement in weld quality will lead to higher productivity and reduced welding costs for the user.
It is another object of this invention to provide an improved gas metal arc welding method which can employ a shielding gas which does not require the presence of a large concentration of helium and yet achieves a comparable improvement in desired weld characteristics.